a. Field of the Invention
This invention relates to a push-pull amplifier circuitry, and more particularly to a simplified circuit arrangement for a multistage direct-coupled push-pull amplifier employing complementary symmetry FET's.
B. Brief description of the Prior Art
Currently known transistorized power amplifiers almost invariably adopt either the full stage direct-coupled circuit configuration, the dual power source system or the pure complementary push-pull circuit configuration which uses complementary symmetry bipolor transistors.
However, there has already hardly been proposed a power amplifier which is constructed by the use of FET's throughout the entire circuitry thereof. This is mainly because of the fact that an FET of a p-channel type is difficult to manufacture and that there has not yet been developed a power FET which is suitable for being employed in the power stage of a power amplifier.
Recently, however, by an application of the known selective oxidization technique which is utilized in the manufacture of large-scale integrated circuits, it has become possible to produce FET's of a p-channel type in a large number on an industrial basis, and along therewith vertical junction-type FET's have come to be put into practice as power FET's. Thus, the conditions for putting into practice a power amplifier which is constructed by the use of FET's entirely in the circuitry as a whole have now become matured.
If, however, these conditions are to follow the circuit configuration of the known power amplifier which employs the conventional bipolar transistors of the current control type, it is not necessarily possible to make full use of the advantageous features of FET's of being controlled by voltage. In particular, an FET is, by nature, not easily affected by the ambient temperature as compared with a bipolar transistor, so that it hardly needs the provision of such means as for making compensation for the variation of the DC bias caused by the variation of ambient temperature. As such, the power amplifier using FET's ought to be constructed by placing an importance on such matters as the simplification of circuit construction, the gain increase, and an improvement in the frequency characteristic.